Bottom Line:
Specifically, the harmonic phenomenon of SSBR was task-related and independent of the neurovascular coupling.These findings suggested that the SSBRs represent non-linear neural oscillations but not brain activations.In comparison with the conventional general linear model, the SSBRs provide us novel insights into the non-linear brain activities, low frequency neural oscillations, and neuroplasticity of brain training and cognitive activities.

Affiliation: Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, 610054, China.

ABSTRACTNeural oscillations are the intrinsic characteristics of brain activities. Traditional electrophysiological techniques (e.g., the steady-state evoked potential, SSEP) have provided important insights into the mechanisms of neural oscillations in the high frequency ranges (>1 Hz). However, the neural oscillations within the low frequency ranges (<1 Hz) and deep brain areas are rarely examined. Based on the advantages of the low frequency blood oxygen level dependent (BOLD) fluctuations, we expected that the steady-state BOLD responses (SSBRs) would be elicited and modulate low frequency neural oscillations. Twenty six participants completed a simple reaction time task with the constant stimuli frequencies of 0.0625 Hz and 0.125 Hz. Power analysis and hemodynamic response function deconvolution method were used to extract SSBRs and recover neural level signals. The SSEP-like waveforms were observed at the whole brain level and at several task-related brain regions. Specifically, the harmonic phenomenon of SSBR was task-related and independent of the neurovascular coupling. These findings suggested that the SSBRs represent non-linear neural oscillations but not brain activations. In comparison with the conventional general linear model, the SSBRs provide us novel insights into the non-linear brain activities, low frequency neural oscillations, and neuroplasticity of brain training and cognitive activities.

f1: The grand-average of task evoked SSBRs at the whole brain level.SSBRs are shown by the mean power at 0.0625 Hz, 0.125 Hz and 0.1875 Hz before (A) and after (B) HRF deconvolution. In a 0.005 Hz bandwidth, SSBRs were significantly induced at 0.06–0.065 Hz (p <0.001) and 0.1225–0.1275 Hz (p <0.001) frequency bands for the LF condition, and at 0.1225–0.1275 Hz (p <0.001) for the HF condition (C). There was no remarkable effect from HRF deconvolution (p >0.05). LF: lower frequency condition; HF: higher frequency condition; error bars represent the 95% confidence interval.

Mentions:
A SSEP-like waveform was shown in Figure 1A. The HRF deconvolution changed the energy distribution along frequency ranges, but did not eliminate SSBRs (Figure 1B). This suggests that the SSBRs are independent of neurovascular coupling. Comparing to the resting state, the LF condition significantly increased the power within 0.06–0.065 Hz [before deconvolution (BD): t (25) = 6.119, p <0.001; after deconvolution (AD): t (25) = 6.501, p <0.001], 0.1225–0.1275 Hz [BD: t (25) = 4.171, p <0.001; AD: t (25) = 4.297, p <0.001] and 0.185–0.19 Hz [BD: t (25) = 2.442, p = 0.022; AD: t (25) = 2.891, p = 0.008] frequency bands; However, the HF condition remarkably enhanced the power within the 0.1225–0.1275 Hz [BD: t (25) = 6.939, p <0.001; AD: t (25) = 8.580, p <0.001] frequency band. The HRF deconvolution slightly reduced the power [t (25) = 2.154, p = 0.041] at the 0.1225–0.1275 Hz frequency band for the LF condition. These results suggest that SSBRs can be evoked at the fundamental frequency of stimulus and its harmonics. This observation is similar to those of the SSEPs. On the other hand, the HRF did not markedly exert influence on the SSBRs, suggesting that the SSBRs are not requiring the hemodynamic function.

Bottom Line:
Specifically, the harmonic phenomenon of SSBR was task-related and independent of the neurovascular coupling.These findings suggested that the SSBRs represent non-linear neural oscillations but not brain activations.In comparison with the conventional general linear model, the SSBRs provide us novel insights into the non-linear brain activities, low frequency neural oscillations, and neuroplasticity of brain training and cognitive activities.

Affiliation:
Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, 610054, China.

ABSTRACTNeural oscillations are the intrinsic characteristics of brain activities. Traditional electrophysiological techniques (e.g., the steady-state evoked potential, SSEP) have provided important insights into the mechanisms of neural oscillations in the high frequency ranges (>1 Hz). However, the neural oscillations within the low frequency ranges (<1 Hz) and deep brain areas are rarely examined. Based on the advantages of the low frequency blood oxygen level dependent (BOLD) fluctuations, we expected that the steady-state BOLD responses (SSBRs) would be elicited and modulate low frequency neural oscillations. Twenty six participants completed a simple reaction time task with the constant stimuli frequencies of 0.0625 Hz and 0.125 Hz. Power analysis and hemodynamic response function deconvolution method were used to extract SSBRs and recover neural level signals. The SSEP-like waveforms were observed at the whole brain level and at several task-related brain regions. Specifically, the harmonic phenomenon of SSBR was task-related and independent of the neurovascular coupling. These findings suggested that the SSBRs represent non-linear neural oscillations but not brain activations. In comparison with the conventional general linear model, the SSBRs provide us novel insights into the non-linear brain activities, low frequency neural oscillations, and neuroplasticity of brain training and cognitive activities.